Alkali resistant refractories

ABSTRACT

An alkali-resistant refractory material has a surface layer characterized by a greater concentration of lithium than the bulk refractory material.

The United States Government has rights in this invention pursuant tocontract no. DE-AC05-00OR22725 between the United States Department ofEnergy and UT-Battelle, LLC.

FIELD OF THE INVENTION

The present invention relates to refractory materials that are resistantto alkali attack, and more particularly to refractory materials having alithium rich surface treatment that retards degradation of refractoriesupon exposure to alkali-rich molten salts particularly molten Na₂CO₃.

BACKGROUND OF THE INVENTION

Gasification of black liquor produced at paper mills during the pulpingprocess is an attractive process of recovering inorganic materials whilegenerating electrical power/steam/biofuels/hydrogen from the wastestream. The process has been delayed in development due to poorresistance of containment materials to alkali attack during long-termoperations. Degradation of refractory and metallic containment materialsin pilot-scale and demonstration-scale gasifiers presents a seriousobstacle to the commercialization of black liquor gasifiers.Gasification vessel refractory linings degrade rapidly (6 months to ayear), requiring replacement. Alkali resistant containment materialscould extend the lifetime of refractory liners, making black liquorgasification a more attractive alternative to recovery boilers.

OBJECTS OF THE INVENTION

Accordingly, objectives of the present invention include provision ofalkali resistant refractory containment materials for high-temperaturevessels, and especially for black liquor gasification processes in orderto make such processes more feasible. Further and other objects of thepresent invention will become apparent from the description containedherein.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, the foregoingand other objects are achieved by an article that includes a refractorymaterial having a surface layer characterized by a greater concentrationof lithium than the refractory material.

In accordance with another aspect of the present invention, a method ofmaking an alkali-resistant material includes the steps of: applying to arefractory material at least one lithium-containing material; andheating the refractory material to a sufficient temperature so that thelithium-containing material forms an alkali-resistant surface layer onthe refractory material.

In accordance with a further aspect of the present invention, a methodof forming an alkali-resistant layer on a refractory vessel linerincludes the steps of: providing a working material including lithium;and heating the working material in the vessel to a sufficienttemperature so that the lithium forms an alkali-resistant surface layeron the vessel liner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of a test sample, after immersion testing inmolten high alkali smelt, of refractory material having a lithium-richlayer in accordance with the present invention.

FIG. 2 is a photograph of a control sample, after immersion testing inmolten high alkali smelt, of refractory material as received from themanufacturer and without a lithium-rich layer.

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure and appended claims in connection withthe above-described drawings.

DETAILED DESCRIPTION OF THE INVENTION

Any lithium-containing composition having a low melting point (less than1300° C.), for example, LiOH and Li₂CO₃, is applied, either as a powderor as a paste formed from a mixture of powder and fluid, to the surfaceof alumina and alumino-silicate refractories. The lithium-containingcomposition is subsequently reacted at a temperature in the range of700° C. to 1300° C. to produce an adherent, lithium-rich surface layer.The surface layer is generally characterized as having a higherconcentration of lithium than the bulk refractory.

The surface layer is resistant to chemical attack by alkaline species,and protects the underlying bulk refractory material from chemicalattack by alkaline species. The surface layer retards the degradation ofrefractory materials exposed to alkali-rich molten smelts, for example,molten Na₂CO₃/Na₂S. The surface layer generally comprises crystallineand/or glassy phases which may include at least one of the followingclasses of compounds: lithium aluminates, lithium silicates, and lithiumalumina silicates, depending on composition of the starting refractorymaterial. The surface layer can be altered during molten smelt exposureto form a layer material that appears to further retard sodium ionpenetration.

EXAMPLE I

An approximately 2 mm thick layer of dry Li₂CO₃ was applied to thesurfaces of mullite/SiO₂ refractory materials. The refractory and Li₂CO₃layer was heated in air to a temperature of 900° C. for one hour toaffect the desired reaction and formation of a lithium-rich surfacelayer on the refractory material. Subsequent x-ray examination of thesurface revealed the formation of crystalline eucryptite (Li₂Al₂SiO₆)and LiAlO₂.

EXAMPLE II

A sample of refractory material prepared in accordance with Example Iand an untreated control sample were immersed for 50 hours at 1000° C.in high alkali molten salt containing Na₂CO₃ and Na₂S. Cross sectionswere subsequently cut from the samples. An improvement in alkaliresistance was observed for the sample having a lithium-rich surfacelayer, shown in FIG. 1, compared to the untreated control sample, shownin FIG. 2.

Other refractory materials such as: alumina, mixed α-β-alumina, andmagnesium-alumina-spinel based refractories have shown some improvedresistance to molten alkali salts after a lithium treatment though notto the extent observed for mullite-based refractories. As the lithiumreacts with the alumina and/or silica minerals present in the refractoryit forms a lithium-rich layer. On immersion in molten alkali salts,degradation of the refractory is retarded.

The present invention can be used to coat individual firebricks and/orhigh-temperature vessel liners. A damaged or worn lithium-rich layer canbe repaired by re-application thereof by any of the processes describedherein. The present invention can significantly extend the life ofrefractory materials.

In other embodiments of the present invention, a solution containingLi₂CO₃, LiOH and/or other lithium composition(s) can be infused viacapillary action into the refractory body prior to heating between 700°and 1300° C. and subsequent formation of lithium-rich layer. Moreover,molten Li₂CO₃ or LiOH can be infused into the refractory with thesubsequent formation of a lithium-rich layer.

EXAMPLE III

A solution containing Li₂CO₃ is applied to the surface of a mullite/SiO₂refractory material and allowed to infuse thereinto. The Li₂CO₃-infusedrefractory is heated in air to a temperature of 900° C. for one hour toaffect the desired reaction and formation of a lithium-rich layer on therefractory material.

Moreover, a slurry of Li₂CO₃ and/or LiOH or a lithium-containingcomposition could be applied to the refractory lining and heated inplace to form lithium compounds on the surface.

EXAMPLE IV

An aqueous slurry of Li₂CO₃ is sprayed onto the surface of amullite/SiO₂ refractory material. The Li₂CO₃-coated refractory is heatedin air to a temperature of 900° C. for one hour to affect the desiredreaction and formation of a lithium-rich layer on the refractorymaterial.

Moreover, Li₂CO₃ and/or LiOH or a lithium-containing composition can beadded to working material, for example, black liquor and/or biomass, andinjected into the gasifier therewith so that during gasification, theformation (new, maintenance, and/or repair) of a lithium-rich layeroccurs on the refractory liner during the biogasification process.

EXAMPLE V

Li₂CO₃ is added to a batch of black liquor prior to injection into agasification vessel. The black liquor is then injected into the gasifierand the biogasification process is carried out therein. In the gasifier,the Li₂CO₃ is deposited on the refractory liner where it reacts with therefractory liner material, forming a lithium-rich layer thereon.

Refractory materials made in accordance with the present invention aresuitable for use as containment materials or as containment liners forapplications where high levels of alkali molten salts are present, forexample, biogasification processes.

While there has been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications can beprepared therein without departing from the scope of the inventionsdefined by the appended claims.

1. An article comprising a refractory material having a surface layercharacterized by a greater concentration of lithium than said refractorymaterial.
 2. An article in accordance with claim 1 wherein said surfacelayer comprises at least one compound selected from the group consistingof lithium aluminate, lithium silicate, and lithium alumina silicate. 3.An article in accordance with claim 1 wherein said surface layer isresistant to chemical attack by alkaline species.
 4. An article inaccordance with claim 1 wherein said surface layer protects saidrefractory from chemical attack by alkaline species.
 5. An article inaccordance with claim 1 wherein said surface layer is adherent to saidrefractory material.
 6. A method of making an alkali-resistant materialcomprising the steps of: a. applying to a refractory material at leastone lithium-containing material; and b. heating said refractory materialto a sufficient temperature so that said lithium-containing materialforms an alkali-resistant surface layer on said refractory material. 7.A method in accordance with claim 6 wherein said lithium-containingmaterial is characterized by a melting point of less than 1300° C.
 8. Amethod in accordance with claim 6 wherein said lithium-containingmaterial further comprises at least one compound selected from the groupconsisting of Li₂CO₃ and LiOH.
 9. A method in accordance with claim 6wherein said applying step comprises depositing a layer of saidlithium-containing material onto said surface.
 10. A method inaccordance with claim 6 wherein said applying step comprises infusingsaid lithium-containing material into said surface.
 11. A method inaccordance with claim 6 wherein said heating step is carried out at atemperature in the range of 700° C. to 1300° C.
 12. A method inaccordance with claim 6 further comprising the additional step of: c.exposing said alkali-resistant material to a working material comprisinglithium in order to maintain said layer.
 13. A method of forming analkali-resistant layer on a refractory vessel liner comprising the stepsof: a. providing a working material comprising lithium; and b. heatingsaid working material in said vessel to a sufficient temperature so thatsaid lithium forms an alkali-resistant surface layer on said vesselliner.
 14. A method in accordance with claim 13 wherein said workingmaterial is characterized by a melting point of less than 1300° C.
 15. Amethod in accordance with claim 13 wherein said working material furthercomprises at least one compound selected from the group consisting ofLi₂CO₃ and LiOH.
 16. A method in accordance with claim 13 wherein saidheating step is carried out at a temperature in the range of 700° C. to1300° C.